Method and device for producing a cylindrical body consisting of quartz glass

ABSTRACT

A known method for producing a cylindrical body uses a precipitation assembly ( 5 ) consisting of several precipitators ( 4 ), to which a parent substance is fed via medium supply lines ( 9 ), whereby the precipitation assembly ( 5 ) completes a closed trajectory ( 6 ) according to a predetermined displacement course, said trajectory comprising at least one precipitation path ( 8 ) that runs along the longitudinal axis ( 2 ) of the support. The aim of the invention is to provide an economical, reproducible, failsafe method based on said known procedure, which enables in particular the production of soot layers ( 3 ) on a support ( 1 ) at a high precipitation rate and nevertheless a high degree of uniformity. To achieve this, the displacement course ( 6 ) comprises a first loop ( 7   a   , 8 ) and a second loop ( 7   b   , 8 ), whereby the completion of the first loop ( 7   a   , 8 ) causes a right-hand torsion in the medium supply lines ( 9 ) and the completion of the second loop ( 7   b   , 8 ) causes a left-hand torsion in said lines ( 9 ).

The present invention relates to a method for producing a cylindricalbody using a deposition assembly consisting of a plurality ofseries-arranged depositors to which a starting substance is fed viamedium supply lines and by means of which particles are deposited inlayers on the outer surface of a carrier rotating about its longitudinalaxis to form the cylindrical body in that the deposition assemblytravels through a closed path of movement in a predetermined movementsequence, the closed path of movement comprising at least one depositionpath extending along the longitudinal axis of the carrier.

Furthermore, the present invention relates to a device which is used forproducing a body and which is suited for carrying out the methodaccording to the invention, the device comprising a deposition assemblyconsisting of a plurality of series-arranged depositors which areconnected to medium supply lines for the supply of a starting substance,and which is movable over a closed path of movement which comprises atleast one deposition path extending along a carrier which is rotatableabout its longitudinal axis.

Cylindrical bodies obtained according to a method of the above-indicatedtype consist, for instance, of ceramics, metal, plastics, or glass,especially of doped or undoped quartz glass. Such quartz glass bodiesare used as preforms for optical fibers, or they are e.g. used in rod ortube form as semifinished products or as start materials in opticalfiber production, especially for optical quartz glass elements for usein microlithography or for producing equipment for the manufacture ofsemiconductors.

The production of synthetic quartz glass for said applications is oftenperformed by flame hydrolysis of suitable silicon-containing startcomponents, especially of silanes or siloxanes according to the knownOVD method (outside vapor deposition). An intermediate product is hereobtained in the form of a tubular “soot body” of porous quartz glass.For the production thereof the silicon-containing start components andfuels (media) are supplied to a deposition burner, they are hydrolyzedin a burner flame to obtain SiO₂ particles, and the particles aredeposited in layers on a carrier rotating about its longitudinal axis,thereby forming the tubular SiO₂ soot body. A quartz glass tube isobtained from the tubular soot body by sintering, and a quartz glass rodis obtained by collapsing the inner bore.

For increasing the deposition rate (SiO₂ mass per time unit), severaldeposition burners may be combined in a row of burners, the row ofburners being reciprocated in parallel with the soot body surface fromone end of the developing blank to the opposite end. In this procedure,however, blank end portions are formed that terminate conically to theoutside and have properties differing from those in the central portion,and they are therefore not usable. The length of said unusable endportions increases with the length of the burner row.

For solving this problem, it is suggested in DE 196 28 958 A1 that aburner assembly should be used, consisting of a plurality of depositionburners which are arranged in a row, and that the burner assembly shouldbe reciprocated in an oscillating manner along the carrier rotatingabout its longitudinal axis, each deposition burner only sweeping over asmall portion of the surface of the soot body. Although soot bodies withend portions tapering to the outside are produced, the size of the endportions does not depend on the length of the burner assembly, but onthe amplitude of the reciprocating movement. It is thereby possible touse an elongated burner row with a plurality of deposition burners andat a correspondingly high deposition rate per time unit. However,inhomogeneities are observed in the regions of the reversal points ofthe burner movement due to local changes in the temperature, due to massdeposition or due to density. Moreover, differences in the depositioncharacteristics of different deposition burners have locally differenteffects on surface temperature and mass deposition, wherebyinhomogeneities are also caused.

These may lead to an irregular surface and may be noticed in adisadvantageous way in the further processing of the soot body and thusdiminish the quality of the quartz glass cylinder obtained from the sootbody, or they require a troublesome reworking. Although this techniqueis characterized by a high deposition rate, the quartz glass cylindersobtained thereby can, without a reworking process, only be used forproducing quartz glass where relatively low demands are made onhomogeneity.

These drawbacks are prevented in the generic method according to U.S.Pat. No. 4,684,384 A, which also discloses a device with theabove-mentioned features. The simultaneous production of several SiO₂blanks from porous quartz glass in a single facility is describedtherein. To this end a plurality of deposition burners are providedthat, circulating one after the other around a closed, substantiallycircular loop (trajectory), deposit SiO₂ particles on the carriers whichare arranged around the trajectory and are rotating about theirlongitudinal axis. The respective blank ends are obtained in this methodby the measure that all deposition burners pivot away one after theother during their circulation around the trajectory from the respectivecarrier to be moved towards the next carrier. The deposition burners donot change their direction of movement in this process, so that all ofthe deposition burners travel through the same trajectory positions timeand again.

This procedure in which it is possible to use an arbitrarily long burnerrow is characterized by a high deposition rate together with asimultaneously high homogeneity of the soot body and the resultingquartz glass cylinder. Nevertheless, this known method has not beenaccepted in practice. The main reason for this must be seen in the factthat the repeating circular movement of the deposition burners requirescomplicated measures for preventing a longitudinal torsion of the mediumsupply lines and a twisting among the same. Two measures are recommendedfor this in U.S. Pat. No. 4,684,384 A. On the one hand, a reciprocatingmovement of the burner row with the above-discussed drawbacks. And onthe other hand the use of a rotary leadthrough to the supply line of themedium flows into the deposition chamber. The rotary leadthrough whichconsists essentially of metallic components and of sealing components isvery complicated constructionally and might satisfy the standard processdemands made on purity, operational reliability and reproducibility onlyto a limited degree because of the chemical aggressiveness of the mediaused (such as SiCl₄).

It is therefore the object of the present invention to provide aneconomic, reproducible and operationally reliable method for producingcylindrical bodies, especially for producing soot layers of SiO₂ on acarrier at a high deposition rate and of high homogeneity at the sametime.

Moreover, it is the object of the present invention to provide aconstructionally simple and inexpensive device which is also suited forcarrying out the method of the invention.

As for the method, this object starting from the above-indicated methodis achieved according to the invention in that the path of movementcomprises a first loop and a second loop, the travel through the firstloop causing a right-hand twisting of the medium supply lines, and thetravel through the second loop causing a left-hand twisting of themedium supply lines.

Without a reversal of the direction of movement, the deposition assemblyrepeatedly travels through a closed path of movement along which one orseveral carriers are arranged for forming one or several bodies. Thetrack of the path of movement along which the depositors cause adeposition of particles on the carrier shall here and in the followingalso be designated as a “deposition path”.

In contrast to the known method, both a reversal of the depositormovement and a rotary leadthrough for the medium supply can be omittedin the method of the invention. Instead of this, a slight twisting ofthe medium supply lines among each other is accepted, but a shearing ortearing off of the lines is prevented in that the deposition assembly inits movement sequence travels through at least two loops having anopposite action on the twisting of the medium supply lines, i.e., atleast one first loop that causes a right-hand twisting of the mediumsupply lines and at least one second loop in which the medium supplylines are subjected to a left-hand twisting. Right-hand twisting andleft-hand twisting compensate each other in the simplest case after eachtravel through the whole path of movement. If after a single travelthrough the path of movement a residual twisting remains in onedirection, its compensation or overcompensation is carried out throughexcessive twisting in the opposite direction during later travel throughthe path of movement. A method accepting a constantly increasingtwisting of the medium supply lines in one direction without offeringthe possibility of untwisting by twisting in the opposite direction isnot the subject of the present invention.

The closed path of movement is defined by the start point of the burnermovement and the subsequent path for returning the deposition assemblyto the start point. For completing a movement sequence within themeaning of the present invention, comprising at least one travel througha first loop with a right-hand twisting and at least one travel througha second loop with a left-hand twisting, the deposition assembly travelsthrough the path of movement once or repeatedly. It is essential that ineach movement sequence at least a section of the path of movement isconfigured as a deposition path, and that the deposition assemblytravels through at least one loop with a right-hand twisting of themedium supply lines and at least one loop with a left-hand twisting ofthe medium supply lines. The medium supply lines are made so flexiblethat they can still absorb the necessary degree of twisting and torsion.Torsion of the individual medium supply lines can also be counteractedby an axially rotatable support of the deposition burners, so that thetorsion of the individual medium supply lines will no longer beconsidered in the following.

The deposition assembly consists of several depositors arranged side byside. The length of the deposition assembly and the number of itsdepositors depend on the length of the path of movement and the lengthof the at least one deposition path. A deposition assembly may be usedthat is shorter than the length of the cylindrical body to be produced,but the deposition assembly is preferably longer than the body, as willbecome apparent from the following explanations. At any rate, due to theuse of a deposition assembly comprising several depositors, a highoverall rate of deposition (per time unit) is achieved. Moreover, thedeposition assembly is always moved from one front end of the developingbody to the opposite front end, so that reversal points of the depositormovement impressed onto the body surface cannot be observed and axiallyhomogeneous material characteristics and a planar surface are therebyachieved. Differences between the depositors do not cause any axialinhomogeneities with respect to density and mass deposition. Moreover, areversal of the direction of movement and the accompanying drawback asto the formation of tapering body ends are also avoided. The method ofthe invention therefore permits a high deposition rate together with anaxially homogeneous distribution of the material characteristics of thebody and an exact cylinder geometry without any significant surfaceundulation.

The method according to the invention is suited for producingcylindrical bodies consisting of different materials, particularly ofSiO₂. The depositors are e.g. configured as flame hydrolysis burners orplasma burners for forming and subsequently depositing particles of thematerial on the carrier, as burners for flame and plasma spraying or asatomization nozzles or injectors for applying layers of powders of therespective material on a carrier. The particles to be deposited on thecarrier are supplied in the depositor or are formed in the depositor.

If the material is quartz glass, a tubular SiO₂ soot body is producedaccording to the method, and a quartz glass tube can be obtained fromsaid body by way of sintering, and a quartz glass rod by collapsing theinner bore thereof. The carrier is normally removed before sintering orcollapsing; otherwise, the soot body is collapsed onto the carrierduring sintering. The carrier is a rod-shaped or tubular body ofgraphite, of a ceramic material such as aluminum oxide, of undopedquartz glass, of doped quartz glass or of doped or undoped porous SiO₂soot. Carriers consisting of doped quartz glass or doped SiO₂ soot mayhere also have a radially inhomogeneous dopant distribution and mayparticularly be configured as semifinished products for optical fibersas a so-called “core rod” with a radially inhomogeneous refractive indexprofile. A particularly preferred variant of the method according to theinvention is characterized in that neighboring depositors of thedeposition assembly keep a desired distance ranging from 5 cm to 50 cmfrom one another, and that during travel through the deposition path thefirst depositor of the deposition assembly follows the last depositor ata distance within the range of the desired distance.

The desired distance of the depositors from one another is within theusual range between 5 cm and 50 cm, but a constantdepositor-to-depositor distance is not required in the depositionassembly. It is essential that in the movement sequence along thedeposition path the first depositor of the deposition assembly alwaysfollows the last depositor at a similar distance as said desireddistance. This can ensure a continuous deposition process on the carrierand prevent an excessive cooling of the body surface, which has anadvantageous effect on the homogeneity of the deposition process andpermits a constant axial mass deposition and a homogeneous densitydistribution. This deposition process, which is as continuous aspossible, shall also be designated in the following as a “uniformfrequentation” of the deposition path. The first depositor of thedeposition assembly need here not follow the last depositor on the samedeposition path. What is of importance is just the axial distance amongthe depositors, for the same effect is achieved due to the rotation ofthe carrier about its longitudinal axis when the first depositor of thedeposition assembly follows the last depositor on a deposition pathextending in parallel therewith.

It has turned out to be advantageous when particles formed by thedepositors outside the deposition path are collected by means of acollection device. The collected particles can be removed from thedeposition chamber so that particles straying therein, which may lead toinhomogeneities upon impingement on the developing body, are reduced.

In a first preferred alternative of the method according to theinvention, the first loop is traveled through in a predetermineddirection of rotation, and the second loop in the opposite direction ofrotation.

In this case the path of movement comprises at least a first loop and asecond loop, each being traveled through in the respectively oppositedirection of rotation. The designations “first loop” and “second loop”as are here chosen do not indicate the sequence in which said loops aretraveled through by the deposition assembly. In the simplest case thedepositors move once around the left side and once around the right side(or vice versa), so that the medium supply lines in each movementsequence are first twisted by 360 degrees and are untwisted againaccordingly when traveling through the subsequent loop. The path ofmovement may also comprise more than two loops. It is important that thetwists caused during travel through the loops can be completelycompensated again in the same or in a later movement sequence.

There are several variants suited for the arrangement of the loopswithin the path of movement. In a first variant, the first loop and thesecond loop have a joint deposition path. This embodiment of the path ofmovement shall also be designated in the following as a “double loop”.

In this case the deposition path forms a section shared by the two loopsalong the path of movement. At the end of the joint section the path ofmovement branches off by “switching” into a right-hand windingpertaining to the first loop or into a left-hand winding pertaining tothe second loop. The two loops may also have several deposition paths incommon. In this method a kind of “switch” is needed, but a crossingpoint between the loops can be avoided, which point requires acorresponding mechanical adaptation of the path of movement and whichparticularly in the case of long deposition assemblies may entailproblems because of the fact that the medium supply lines present mutualobstacles to one another. It has also turned out to be advantageous thatthe deposition assembly always travels through the joint path ofmovement in the same direction of movement, which is conducive to itsuniform frequentation and thus improves the homogeneity of the sootbody.

In a second suitable variant for the arrangement of the loops inside thepath of movement, each of the two loops has a deposition path and theyshare a crossing point. In this variant, the two loops also differ fromeach other in their direction of rotation. At the crossing point thefirst loop and the second loop intersect, and it is not necessary herethat the loops at the crossing point extend in a joint plane. At anyrate the crossing point is obtained in the projection of the path ofmovement onto a plane extending in parallel with the longitudinal axisof the carrier. An overlapping of the loops offers many possiblevariants of design for a closed path of movement within the meaning ofthe invention. The two loops with the opposite direction of rotationform an “8-form” in the simplest case, so that said embodiment of thepath of movement will also be designated in the following as an“8-shaped loop”.

Preference is given to a variant of the method of the invention in whichthe depositors are operated in a deposition mode with deposition ofparticles on the outer cylinder surface of the carrier during travelthrough the deposition path, and in an idle mode without deposition ofparticles.

Thanks to a switching between deposition mode and idle mode, startmaterial and possibly also fuels can be saved. To this end the supply ofsaid media or at least of the start material is stopped or reduced whenthe depositors are outside a deposition path.

In the case of a “double loop”, not more than 50% of the depositors ofthe deposition assembly are advantageously operated in the depositionmode at the same time.

The deposition assembly is here at least twice as long as the partiallength of the deposition assembly with depositors being each operated inthe deposition mode. This helps to homogenize the deposition process onthe carrier and thus to observe an approximately identical temperatureof the body surface in the case of heating depositors. This requiresthat another depositor will be used at the rear end as soon as the firstdepositor of the deposition assembly leaves the joint deposition path atthe front end to be returned via the one loop towards the rear end.Since the return path to the rear end in a cylindrical body cannot beshorter than the deposition path itself, the deposition assembly musthave at least twice the length of the deposition path.

In the described first alternative of the method of the invention, theright-hand twisting and the left-hand twisting of the medium supplylines is accomplished through correspondingly wound loops of the ofmovement in that the deposition assembly changes its direction (sense)of rotation. In the second preferred alternative of the method of theinvention, which will be explained in the following, the first loopcausing the right-hand twisting and the second loop of the closed pathof movement that causes the left-hand twisting are formed by a suitabledynamic supply of the medium supply lines.

The path of movement comprises a single loop which is traveled throughby the deposition assembly at least once as the first loop and at leastonce as the second loop in the same direction of rotation, the mediumsupply lines or o medium collection line branched into the medium supplylines being shifted in the movement sequence such that when the firstloop is traveled through a right-hand twisting is obtained and when thesecond loop is traveled through a left-hand twisting of the mediumsupply lines or the medium collection line is obtained.

The medium supply lines or a medium collection line branching into themedium supply lines are here shifted during a movement sequence suchthat a left-hand twisting and a right-hand twisting of the medium supplylines or the medium collection line are alternatingly obtained.

When the deposition assembly travels through a wound section of the pathof movement (loop), the direction of twisting of the medium supply linesdepends on the side from which medium supply lines or medium collectionline are fed to the depositors. In one case this yields a left-handtwisting of the medium supply lines among one another, and in the othercase a right-hand twisting. This effect is exploited in the method ofthe invention for preventing excessive twisting of the medium supplylines in that the medium supply lines or the medium collection line arefed to the depositors during a movement sequence, arriving at least oncefrom the one side of the path of movement (from above) and at least oncefrom the opposite side of the path of movement (from below). In thisprocedure the medium supply lines or the medium collection line musttherefore be shiftable from the one side of the path of movement to theother side. A track, which is otherwise closed, is here passed throughby the medium supply lines or the medium collection line in a directiontransverse to the track course. In this variant of the method, a simpleclosed single loop is adequate; a double loop or an 8-shaped loop is notneeded.

In each movement sequence, the single loop is passed through at leasttwice, namely once as the first loop with right-hand twisting and onceas the second loop with left-hand twisting of the medium supply lines orthe medium collection line. This procedure will be illustrated in thefollowing with reference to a simple example: When the depositors travelanticlockwise through a closed single loop forming a horizontal planeand when in this case the medium supply lines are fed from underneaththe horizontal plane to the depositors, this yields a twisting of thelines in one direction. Otherwise, upon supply of the medium supplylines from above the horizontal plane and through the path of movement,this yields a twisting in the other direction. The medium supply linesare e.g. shifted according to predetermined time intervals, independence upon the position of the deposition assembly on the path ofmovement, after a non-recurring travel or after repeated travels throughthe path of movement, if necessary, or statistically. A previouslyproduced twisting of the medium supply lines is compensated orovercompensated completely or in part after the shifting thereof.

Said shifting of the medium supply lines is particularly simple when theindividual medium supply lines are bundled into a medium collection linewhich branches at a branch point into the medium supply lines connectedto the depositors.

For changing the twisting direction of the individual medium supplylines connected to the depositors, the medium collection line must justbe shifted such that it is supplied once from the one side to the pathof movement and once from the other side. The medium collection line ise.g. configured as a bundle of the individual medium supply lines and inthis case the medium supply lines are just distributed at the branchpoint, or the medium collection line contains a single line for each ofthe media to be supplied to the depositors (starting substances, fuels).In this case a container from which the individual medium supply linesbranch off is provided at the branch point. The branch point ispreferably positioned near the plane of the path of movement; a shiftingof said branch point is however not required for causing a right-hand ora left-hand twisting of the medium supply lines or the medium collectionline. What is essential for the direction of twisting after shifting isthe course of the lines directly in front of the depositors.

It has turned out to be particularly useful when the shifting of themedium supply lines or the shifting of the medium collection linecomprises a passing through the path of movement.

During shifting the path of movement is traversed by the individualmedium supply lines or by the medium collection line, the path ofmovement comprising a suitable passage for this purpose, for instance inthe form of a permanent or closable gap. After passage of the mediumsupply lines or the medium collection line a reversal of the formertwisting direction is achieved for said lines.

Preferably, the single loop is completely occupied by the depositors ofthe deposition assembly in this variant.

The complete occupation with depositors permits a continuous depositionwithout interruption by gaps in the deposition assembly and thus ahomogeneous temperature action on the body or bodies when heatingdepositors are used, such as deposition burners in the form of plasmaburners or flame hydrolysis burners. This procedure has a particularlyadvantageous effect whenever several carriers on which materialparticles are deposited are arranged one after the other along the pathof movement.

In the simplest case the medium supply lines or the medium collectionline is each time shifted once during travel through the path ofmovement.

The path of movement is here traveled through fully or alternatingly inthe case of medium supply lines arriving from the one side and in thecase of medium supply lines arriving from the other side. The mediumsupply lines or the medium collection line may here traverse theabove-mentioned permanent or temporarily existing gap of the path ofmovement before or after the deposition assembly passes through saidgap.

The method can be performed in a particularly simple way when the mediumsupply lines or the medium collection line are shifted alternatinglyafter having passed once through the first loop and the second loop.

It has turned out to be advantageous when before each passage throughthe path of movement the medium supply lines have a preliminary twistingwith a twisting direction opposite to the twisting direction in thesubsequent passage through the path of movement.

Hence, during each passage through the path of movement a previouslyexisting twisting is overcompensated in the opposite direction. Ideally,the twisting of the medium supply lines can thus be limited to 180degrees in the one and in the other direction.

The two above-described alternatives of the method are further improvedif at least two carriers rotating about their respective longitudinalaxis are provided along the path of movement, the path of movementcomprising at least one deposition path extending along each carrier.

Starting from the deposition path that is the first one, the depositionassembly can here be returned at the beginning of the first depositionpath via a further second deposition path. This prevents an idleoperation of the depositors and increases the overall deposition rate.

It has turned out to be advantageous when the at least two carrierscomprise longitudinal axes extending in parallel with one another.

The parallel arrangement of the carriers yields a short length of thepath of movement. This is particularly true for the use of two carrierswhereas in the case of three or more carriers polygonal arrangements mayalso be of advantage.

In the alternative of the method with a shifting of the medium supplylines, a further improvement is achieved when each of the depositors hasassigned thereto a main deposition direction which extends inclined bynot more than 30 degrees relative to a plane formed by the carriers.

With a corresponding orientation of the depositors in said plane, aheating up of the medium supply lines (or the collection line) can bediminished during their shifting in the case of heating depositors.

Moreover, two deposition paths that are opposite to the each other onthe path of movement and are interconnected through 180-degree arcs witha small radius can thereby be realized. Small 180-degree arcs ensure aminimum idle running of the depositors or a low loss of start material.In the simplest case two carriers arranged along a path of movement forma horizontally oriented plane of the path of movement. The maindeposition direction extends in this case also horizontally, or itextends upwards slightly inclined with an inclination angle of not morethan 30 degrees relative to the horizontal. In the case of depositors inthe form of deposition burners the main propagation directioncorresponds to the main propagation direction of the respective burnerflame.

As for the device, the above-indicated object starting from a device ofthe above-indicated type is achieved according to the invention in thatthe path of movement comprises a first loop causing a right-handtwisting of the medium supply lines, and a second loop causing aleft-hand twisting of the medium supply lines.

Without a reversal of the direction of movement the deposition assemblypasses repeatedly through a closed path of movement along which one orseveral carriers are arranged for forming a deposition body or severalcylindrical deposition bodies.

In contrast to the known device, a rotary leadthrough for the supply ofthe starting substances is omitted in the device of the invention.Instead of this, a slight twisting of the medium supply lines among oneanother is accepted, but a shearing or tearing off of the lines isprevented in that the deposition assembly in its movement sequencepasses through at least two loops having an opposite effect on thetwisting of the medium supply lines, namely at least one first loopcausing a right-hand twisting of the medium supply lines and at leastone further second loop in which the medium supply lines are subjectedto a left-hand twisting. In the simplest case, right-hand twisting andleft-hand twisting completely offset one another during each passagethrough the path of movement. If a residual twisting remains in onedirection after a non-recurring travel through the path of movement, acompensation or overcompensation thereof is effected by an excessiveopposite twisting in the subsequent travel through the path of movement.

The closed path of movement is defined by the start point of the burnermovement and the subsequent path for returning the deposition assemblyto the start point. For completing a movement sequence in the sense ofthe invention the deposition assembly travels through the path ofmovement once or repeatedly. It is essential that in each movementsequence at least one section of the path of movement is configured asthe deposition path and that the deposition assembly passes through atleast one loop with right-hand twisting of the medium supply lines andat least one loop with left-hand twisting of the medium supply lines.The medium supply lines are configured to be so flexible that they canabsorb the required degree of twisting and torsion. The torsion of theindividual medium supply lines can also be counteracted by an axiallyrotatable support of the depositors, so that the torsion of theindividual medium supply lines will no longer be considered in thefollowing.

The deposition assembly consists of several depositors arranged side byside. These are e.g. flame hydrolysis burners or plasma burners for theformation and subsequent deposition of particles of the material on thecarrier, or burners for flame and plasma spraying or atomization nozzlesor injectors for applying layers of powders of the respective materialon the carrier.

The length of the deposition assembly and the number of its depositorsdepends on the length of the path of movement and the length of the atleast one deposition path. A deposition assembly may be used that isshorter than the length of the body to be produced, but preferably thedeposition assembly is longer than the body. In each case a high overallrate of deposition (per time unit) is achieved due to the use of adeposition assembly comprising several depositors. Moreover, thedeposition assembly is always moved from a front end of the developingbody to the opposite front end, so that reversal points of the depositormovement impressed onto the body surface do not occur, and axiallyhomogeneous material properties and a planar surface are thus achieved.Moreover, a reversal of the direction of movement and the accompanyingdrawback with respect to the formation of tapering body ends are therebyavoided as well. Therefore, the device according to the inventionpermits a high deposition rate together with an axially homogeneous massdeposition and a homogeneous distribution of the materialcharacteristics of the deposition body and thus an accompanying exactcylinder geometry without any significant surface undulation; thedrawbacks resulting from a rotary leadthrough with respect toconstructional expense and poor operational reliability andreproducibility are thereby avoided.

Further advantageous developments of the device of the invention becomeapparent from the subclaims. Insofar as configurations of the deviceindicated in the subclaims imitate the procedures mentioned in subclaimsregarding the method of the invention, reference is made forsupplementary explanation to the above observations made on thecorresponding method claims.

Further advantageous modifications of the device of the invention shallnow be explained:

Advantageously, in the case of a device having at least one first loopand at least one second loop, the first loop and the second loop havethe same length.

This guarantees that the residence time of the deposition assembly ineach of the loops is the same, so that a uniform frequentation of thedeposition path or the deposition paths by the deposition assembly ismade possible. This is promoted when the loops have the same lengths orwhen the length of the deposition assembly is adjusted according to theloop length, reduced by a depositor-to-depositor distance.

For carrying out the above-described variant of the method with shiftingof the medium supply lines during the movement sequence, one embodimentof the device according to the invention has turned out to be useful inwhich the path of movement comprises a closed single loop which istraveled through by the burner assembly at least once as the first loopand in the same direction of rotation at least once as the second loop,and that a means is provided for shifting the medium supply lines or amedium collection line branching into the medium supply lines, in such amanner that the medium supply lines or the medium collection line extendto the depositors during a movement sequence, alternatingly arrivingfrom one side of the closed single loop and from the opposite side ofthe single loop.

Depending on whether the medium supply lines or the medium collectionline extend from the one side or from the opposite side of the path ofmovement to the depositors, this will once yield a left-hand twistingand once a right-hand twisting. Reference is made to the aboveexplanations regarding the method according to the invention.

A particularly preferred design of the device of the invention with atleast two carriers having longitudinal axes extending in parallel witheach other is characterized in that the distance of the longitudinalaxes of the carriers can be enlarged.

It is thereby possible to keep constant the distance between thedepositors and the surface of the deposition bodies which are formed onthe carriers and get larger.

Stationary additional heaters in the region of the body ends accomplisha consolidation of particularly porous ends, which improves themechanical stability of the deposition body.

One embodiment of the device according to the invention has turned outto be particularly advantageous, wherein the depositors have each acentral axis, the depositors being each rotatably supported about thecentral axis in a mount connected to the path of movement.

Thanks to the rotatable supporting of the depositors the torsion of theindividual medium supply lines relative to the depositors is reducedduring travel through the path of movement.

The invention shall now be explained in more detail with reference toembodiments and a drawing which schematically shows in detail in

FIG. 1 a device for carrying out the method of the invention, includinga path of movement in the form of a double loop with a joint path ofdeposition, in a view from below onto the carrier;

FIG. 2 a second variant of the device including a path of movement inthe form of an 8-shaped loop and with two deposition paths, in a viewfrom below onto the carrier;

FIG. 3 a variant of the device according to FIG. 2, in a view onto thefront side of the longitudinal axis of the carrier;

FIG. 4 a further variant of the device with a path of movement in theform of a single loop and medium supply lines which can be displacedaround a plane of the path of movement, in a top view;

FIG. 5 the variant of FIG. 4 in a side view; and

FIG. 6 a further variant of the device with a path of movement in theform of a closed single loop with left-hand and right-hand windingsabout four carriers arranged in a square, and with medium supply lineswhich can be displaced around the plane of the path of movement, in atop view.

The arrangement according to FIG. 1 shows a carrier 1 in the form of analuminum oxide tube which rotates about its longitudinal axis 2, asoutlined by the rotational arrows. A porous soot body 3 is formed bymeans of an OVD method (outside vapor deposition) on the carrier 1. Tothis end a total of 16 deposition burners 4 of quartz glass, depositorswithin the meaning of the present invention, are provided that aredisplaced in a row at a distance of 15 cm each in the form of a “burnercoil” 5 along a path of movement 6 with a total length of 4.80 m. Thepath of movement 6 is configured as a rail, as will be explained indetail with reference to FIG. 3. The individual deposition burners 4 ofthe burner coil 5 are interconnected by means of a chain. The path ofmovement 6 has the shape of a double loop, the two loop sections 7 a, 7b having the same length and a joint central section 8 that extends inparallel with the longitudinal axis 2 of the carrier. The length of theburner coil 5 is 2.25 m, which is half the length of the path ofmovement 6 less a burner-to-burner distance of 15 cm, and thus abouttwice the length of the central section 8. The burner coil 5 isrepresented by a continuous bold line, and the part of the path ofmovement 6 that is presently not occupied by deposition burners 4 by athin dotted line. The path of movement 6 is configured in the form of aguide rail for the burner coil 5.

SiCl₄, hydrogen and oxygen are supplied to each of the depositionburners 4 via separate medium supply lines 9. The medium supply lines 9arriving from below extend in the view of FIG. 1 in a directionperpendicular to the sheet plane. They are made from flexible tubes ofPFA (perfluoroalkoxy) or from polytetrafluoroethylene (Teflon). Bothmaterials have turned out to be suitable materials for the formation ofthe medium supply lines for reasons of purity and resistance tochemicals and because of thermal stability.

The method of the invention shall now be explained in more detail withreference to an example and with reference to FIG. 1:

For producing an SiO₂ soot body 3 the deposition burners 4 are fed innominal terms via separate medium supply lines 9 with the same amountsof the media in the form of SiCl₄, oxygen and hydrogen, and each ofthese amounts is converted in a burner flame (whose direction ofpropagation in the illustration of FIG. 1 extends in a directionperpendicular to the sheet plane towards the soot body 3) into SiO₂particles. When traveling through the central section 8, the burnerflames are directed onto the carrier 1 or the surface 11 of the sootbody 3 already formed thereon, so that SiO₂ particles are deposited inlayers by means of the deposition burners 4 onto the carrier 1 withformation of the porous

SiO₂ soot body 3. In this respect the central section 8 is a “path ofdeposition” within the meaning of the invention. During travel throughthe loop sections 7 a, 7 b the SiCl₄ supply to the deposition burners 4is stopped.

The burner coil 5 is moved in a repeating movement sequence withoutreversal of the direction of movement along the path of movement 6. Themovement sequence is sketched by the directional arrows 10. The centralsection 8 of the path of movement 6 is traveled through by the burnercoil 5 in the illustration of FIG. 1 always from the left to the rightside, and it is only in the central section 8 that SiO₂ particles aredeposited on the outer cylindrical surface 11 of the soot body 3. At theright end 12 of the central section 8, the path of movement 6 branchesonce into the loop section 7 a wound to the left side and during thenext travel into the loop section 7 b wound to the right side. In theembodiment, the following movement sequence is obtained: The burner coil5 travels through the central section 8 from the start point 13 (leftend of the central section 8) to the end 12 (right end of the centralsection 8) and first terminates there in the loop section 7 a wound tothe left side, through which the burner boil 5 is returned again to thestart point 13. So far this has led to a left-hand twisting of themedium supply lines 9 by 360 degrees. The last deposition burner 4 ofthe burner coil 5 is provided with an arm which activates a switch.After having traveled through the central section 8 again, the burnercoil 5 therefore terminates in the loop section 7 b which is wound tothe right side and through which it is returned again to the start point13 where the next movement sequence will start. During travel throughthe loop section 7 b the left-hand twisting of the medium supply lines 9is fully compensated, so that at the end of each movement sequence themedium supply lines 9 are untwisted. The length of the burner coil 5 ischosen such that the foremost deposition burner 4 starts at a distanceof about 15 cm from the last deposition burner 4 of the burner coil 5 atthe start point 13 in the middle section 8.

This permits a continuous movement sequence of the burner coil 5 withoutreversal of the direction of movement and without cooling of the sootbody 3, the medium supply lines 9 being twisted by 360 degrees at themost. With a preliminary twisting of the medium supply lines by e.g. 180degrees to the right, the initial left-hand twisting can be halvedduring travel through loop section 7 a, and thus also the maximumtwisting on the whole.

The method according to the invention permits a homogeneous depositionof the SiO₂ particles at a high deposition rate, and constructionallycomplicated rotary leadthroughs for the medium supply can be omitted.

If the same reference numerals as in FIG. 1 are used in FIGS. 2 to 6,these designate identical or equivalent parts of the device as thecorresponding reference numerals in FIG. 1. Detailed explanations followfrom the above observations.

In the device shown in FIG. 2, a carrier 1 is shaped in the form of analuminum oxide tube which rotates about its longitudinal axis 2. Aporous soot body 3 is formed by means of an OVD method (outside vapordeposition) on carrier 1. To this end a total of 18 deposition burners 4of quartz glass are provided and displaced in a row at a distance of 10cm each in the form of a “burner coil” 5 along a path of movement 6. Thepath of movement 6 has the form of an 8-shaped loop, consisting of thetwo loop sections 27 a, 27 b that intersect at a crossing point 21. Thetwo loop sections 27 a and 27 b have the same length. Each has adeposition path 28 a, 28 b which extends in parallel with thelongitudinal axis 2 of the carrier. The length of the burner coil 5 andthe lengths of the loop sections 27 a, 27 b are matched with one anothersuch that the first deposition burner 4 b on the one deposition path 28b follows the last deposition burner 4 a on the other deposition path 28a at a distance of 10 cm. The length of the burner coil 5 is half thelength of the path of movement 6 less a burner-to-burner distance of 10cm, which is 170 cm in this specific case. The deposition path 28 b andthe deposition path 28 a are traveled through by the deposition burners4 in the same direction (from the right to the left), as outlined bydirectional arrows 10. The crossing point 21 is within a region outsidethe deposition paths 28 a, 28 b. The crossing point 21 at which the loopsections 27 a and 27 b cross each other is constructed as a simple railcrossing.

SiCl₄, hydrogen and oxygen are supplied to each of the depositionburners 4 via separate medium supply lines 9. The medium supply lines 9arriving from below extend in the view of FIG. 2 in a directionperpendicular to the sheet plane. They are made from flexible tubes ofPFA.

The method of the invention shall now be explained in more detail withreference to an example and with reference to FIG. 2:

For producing an SiO₂ soot body 3 the deposition burners 4 are fed withnominally identical amounts of the media in the form of SiCl₄, oxygenand hydrogen, and each of these amounts is converted in a burner flame(whose direction of propagation in the illustration of FIG. 2 extends ina direction perpendicular to the sheet plane towards the soot body 3)into SiO₂ particles. When traveling through the deposition paths 28 a;28 b, the burner flames are directed onto the carrier 1 or the surface11 of the soot body 3 already formed thereon, so that SiO₂ particles aredeposited in layers by means of the deposition burners 4 on the carrier1 with formation of the porous SiO₂ soot body 3. During travel throughthe loop sections 27 a; 27 b outside the deposition paths 28 a; 28 b,the SiCl₄ supply to the deposition burners 4 is stopped. Thosedeposition burners that are not fed with SiCl₄ at the moment areprovided with a brighter hatching.

The burner coil 5 is moved in a repeating movement sequence withoutreversal of the direction of movement along the path of movement 6. Themovement sequence is symbolized by the directional arrows 10. In theembodiment, the following movement sequence is obtained:

The burner coil 4 is given a left-hand twisting of minus 180 degreesbefore start of the first travel.

Starting at the right end of the soot body 3, it travels through thedeposition path 28 a and through the loop section 27 a wound to theright side, with the result that the preliminary twisting of the mediumsupply lines 9 is compensated, it then crosses the crossing point 21 andsubsequently travels through the deposition path 28 b with a right-handtwisting of 180 degrees. The deposition path 28 b extends, offset byabout 4 cm, in parallel with the deposition path 28 a along the carrier1. From the deposition path 28 b the burner coil 5 passes over the loopsection 27 b, which is wound to the left side by 180 degrees, back tothe crossing point 21, with the result that the twisting of the mediumsupply lines 9 is offset at the crossing point 21, and it is again giventhe initial left-hand twisting of minus 180 degrees when passing ontothe deposition path 28 a. This permits a continuous movement sequence ofthe burner coil 5 without reversal of the direction of movement andwithout cooling of the soot body 3, the medium supply lines 9 beingtwisted by not more than 180 degrees to the left side and to the rightside.

Each of the deposition paths 28 a and 28 b extends laterally offset byabout 2 cm relative to the longitudinal axis 2, as is schematicallyoutlined in FIG. 3. The figure is a view showing the device of FIG. 2 inthe direction of the longitudinal axis of the carrier and in aprojection of the two deposition burners 4 a and 4 b, which are arrangedone after the other on different deposition paths 28 a and 28 b inlongitudinal axis direction, onto a joint plane (sheet plane). Thedistance of 2 cm, based on the vertical 24 (central axis), refers to theminimum distance of the opposite rails 14 from each other. Whentraveling through the deposition paths 28 a and 28 b, respectively, thedeposition burners are here inclined relative to the vertical 24, as isalso shown in FIG. 3. The inclination of the deposition burners 4 ishere adjusted such that the extension of the main propagation direction23 of the burner flames 26 intersects the longitudinal axis 2. The rail14 comprises two metal rods extending in parallel with one another andalong the path of movement 6. The mounting and guidance of thedeposition burners 4 a, 4 b on the rail 14 consists of an inner part 15,to which the quartz glass deposition burners 4 are firmly fixed, and ofan outer part 16 which has a receiving means into which the inner part15 projects and in which it is rotatably supported axially (about themain propagation direction 23), as outlined by rotational arrow 18. Theouter part 16 simultaneously serves to guide the deposition burner 4 a,4 b on the rail 14. Thanks to the rotational support of all depositionburners 4, the torsion of the individual medium supply lines 9 relativeto the deposition burners 4 is reduced during travel through the path ofmovement 6.

The method of the invention permits a homogenous deposition of the SiO₂particles at a high deposition rate and without constructionallycomplicated rotary leadthroughs for the medium supply.

In the embodiment of the device of the invention according to FIG. 4,the deposition burners 4 are guided in a single loop 30. The single loop30 comprises two deposition paths 31, 21 b extending along two sootbodies 3, which are interconnected via curved ends 34. Two oppositelyrotating carriers 1 with longitudinal axes 2 arranged in parallel witheach other are arranged along the deposition paths 31 a, 31 b. Thesingle loop 30 defines a horizontally oriented burner plane 32, which inthe embodiment corresponds to the plane of the drawing sheet. The lengthof the burner coil 5 extends over the whole path of movement 6, thedistance of neighboring burners being 10 cm.

In the method of the invention, a twisting of the medium supply lines 9is prevented by a compensating movement in which the medium supply lines9 are supplied alternatingly once from above the burner plane 32 to thedeposition burners 4 and once from below to the burner plane 32. Themedium supply lines are here bundled into a medium collection line 33which branches at a branch point 37 into the individual medium supplylines 9. The alternating movement of the medium collection line 33 canclearly be seen in FIG. 5. As a consequence, the single loop 30 is oncetraveled through as the first loop 30 a with right-hand twisting of themedium supply lines and after the displacement of the medium supplylines 9 the next time as the second loop 30 b with left-hand twisting ofthe medium supply lines 9.

In this procedure the two soot bodies 3 are arranged such that thelongitudinal axes 2 of the respective carriers 1 extend in parallel withone another and in the burner plane 32. The soot bodies 3 are acted uponby the deposition burners 4 at the same angle. This is necessarywhenever the two soot bodies 3 should have identical characteristicswith respect to density and mass without the medium supply beingadapted. In the specific embodiment, the deposition burners 4 aredirected onto the soot body surface 11 such that the main propagationdirection of the burner flames also extends in the burner plane 32, i.e.horizontally. This arrangement of the deposition burners 4 offers theadvantages that the deflection of the deposition burners 4 in the areaof the two curved ends 34 of the path of movement 6 is just carried outby simply pivoting the deposition burners 4 in the burner plane 32, forwhich a short distance (narrow radius of curvature) and acorrespondingly short period of time for traveling through the ends 34are needed, so that, as a result, SiO₂ is hardly lost, and a heating ofthe medium supply lines 9 extending above the deposition burners 4 or ofthe medium collection line 33 is mainly avoided.

A stationary additional burner 38 is provided at each of the two frontends of the soot body 3. With the help of this additional heater 38 theends of the soot body 3 are consolidated and their mechanical strengthis thereby improved.

During displacement of the medium collection line 33, said line is movedin the area of the one of the two curved ends 34 of the path of movement6 through the opening 35 thereof. In the area of the opposite curved end34 of the path of movement 6, a collection device 39 is provided forcollecting SiO₂ particles produced by the deposition burners 4 whilechanging from the one deposition path to the other, thereby removingsaid particles from the surroundings of the soot body 3. FIG. 5 shows indetail that the individual medium supply lines 9 are first combined inthe middle of the burner assembly 6 to form a medium collection line 33.With a permanent position of the medium collection line 33, said linewould be further twisted with each rotation. This is prevented in thatthe medium collection line 33 is each time passed through a gap 35 inthe path of movement 6 from the top to the bottom, and vice versa, whenthe last deposition burner 4 of the burner coil 5 has passed through thegap 35. The complete sequence of movement thus consists in this case oftwo travels of the burner coil 5 around the path of movement 6, themedium collection line 3 being guided during the first travel from abovethrough the burner plane 32 and supplied during the second travel fromunderneath the burner plane 32 to the deposition burners 4.

This variant of the method according to the invention also permits ahomogeneous deposition of the SiO₂ particles at a high deposition rate,and constructionally complicated rotary leadthroughs for the mediumsupply can here be omitted.

The embodiment of the device of the invention according to FIG. 6 showsa modification of the device illustrated in FIGS. 4 and 5. In thismodification four carriers 1 are arranged in a square along a closedpath of movement 6. The deposition burners 4 of the burner coil 5 travelthrough the path of movement 6 with a right-hand rotation in thedirection illustrated by way of directional arrows 10 and at aburner-to-burner distance of 15 cm, the path of movement 6 comprisingfour deposition paths 58 a, 58 b, 58 c and 58 d. The path of movement 6is fully occupied by deposition burners 4, the distance between thefirst deposition burner 4 a of the burner coil 5 and the last depositionburner 4 b of the burner coil 5 being about 30 cm.

The soot bodies 3 are here arranged such that the longitudinal axes 2 ofthe respective carriers 1 extend in a joint, horizontally extendingburner plane 52. The soot bodies 3 are acted upon from below by thedeposition burners 4 in a direction perpendicular to the burner plane52. This orientation of the deposition burners 4 has the advantage thatupon deflection of the deposition burners 4 in the area of the curvedportions 51 of the path of movement 6 a change is not needed in theorientation of the deposition burners 4 relative to the burner plane 52.

For the sake of clarity, FIG. 6 only shows some of the individual mediumsupply lines 9. The medium supply lines 9 are bundled into a mediumcollection line 37 and branch off in a branch point 37. With a constantlinear guidance of the medium supply lines 9, these would get furthertwisted with each travel of the burner coil 6. This is avoided accordingto the invention in that each time when the last deposition burner 4 bhas passed through a gap 35 in the path of movement 6, the medium supplyline 33 is shifted and thereby guided through the gap 35, as illustratedby directional arrow 35, so that the medium supply lines 9 are guidedonce from underneath the burner plane 52 and once from above through theburner plane 52 towards the deposition burners 4, each displacement ofthe medium supply lines causing a reversal of the twisting. Hence, inthis case, too, the complete movement sequence consists of twocirculations of the burner coil 5 around the path of movement 6, themedium collection line 33 being guided during the first circulation fromabove through the burner plane 32, and during the second circulationfrom underneath the burner plane 32 to the deposition burners 4.

This variant of the method according to the invention also permits ahomogeneous deposition of SiO₂ particles at a high deposition rate, andconstructionally complicated rotary leadthroughs for the medium supplycan be omitted.

1. A method for producing a cylindrical body using a deposition assemblyhaving a plurality of serially-arranged depositors to which a startingsubstance is fed via medium supply lines, said method comprising:depositing particles in layers on an outer surface of a carrier rotatingabout a longitudinal axis thereof to form the cylindrical body, whereinthe deposition assembly travels through a closed path of movement in apredetermined movement sequence, said path of movement comprising atleast one deposition path extending along the longitudinal axis of thecarrier, wherein the path of movement comprises a first loop and asecond loop, the deposition assembly, when traveling through the firstloop causing a right-hand twisting of the medium supply lines, and whentravelling through the second loop causing a left-hand twisting of themedium supply lines.
 2. The method according to claim 1, whereinneighboring depositors of the deposition assembly are maintained at apredetermined distance that is in a range of 5 cm to 50 cm from oneanother, and wherein during travel through the deposition path a firstdepositor of the deposition assembly follows a last depositor thereof ata distance within the range of the predetermined distance.
 3. The methodaccording to claim 1 wherein particles deposited by the depositorsoutside the deposition path are collected by means of a collectiondevice.
 4. The method according to claim 1, wherein the first loop istraveled through in a predetermined direction of rotation, and thesecond loop in an opposite direction of rotation.
 5. The methodaccording to claim 4, wherein the first loop and the second loop have ajoint path of deposition.
 6. The method according to claim 4, whereinthe loops have a crossing point in common and each has at least one pathof deposition.
 7. The method according to claim 1, wherein thedepositors are operated in a deposition mode so as to cause depositionof particles on the outer cylindrical surface of the carrier duringtravel through the deposition path and in an idle mode withoutdeposition of particles.
 8. The method according to claim 7, wherein notmore than 50% of the depositors of the deposition assembly aresimultaneously operated in the deposition mode.
 9. The method accordingto claim 1, wherein the path of movement comprises a single loop whichis traveled through by the deposition assembly at least once as thefirst loop and at least once as the second loop in the same direction ofrotation, the medium supply lines or a medium collection line branchinginto the medium supply lines, being displaced in the movement sequencesuch that during travel through the first loop a right-hand twisting ofthe medium supply lines or the medium collection line is produced andduring travel through the second loop a left-hand twisting of the mediumsupply lines or the medium collection line is produced.
 10. The methodaccording to claim 9, wherein the medium supply lines are bundled into amedium collection line which branches at a branch point into the mediumsupply lines connected to the depositors.
 11. The method according toclaim 9, wherein the medium supply lines or the medium collection lineare displaced by a guiding thereof through the path of movement.
 12. Themethod according to claim 9, wherein the depositors of the depositionassembly are distributed throughout the single loop.
 13. The methodaccording to claim 9, wherein the medium supply lines or the mediumcollection line are alternately displaced after having traveled oncethrough the first loop and once through the second loop, respectively.14. The method according to claim 9, wherein before each travel throughthe path of movement the medium supply lines have a pre-twisting with atwisting direction opposite to the twisting during subsequent travelthrough the path of movement.
 15. The method according to claim 9,wherein at least one further carrier rotating about a respectivelongitudinal axis thereof is provided along the path of movement, andthat the path of movement comprises, extending along each furthercarrier, a respective deposition path.
 16. The method according to claim15, wherein the longitudinal axes of the carriers extend in parallelwith each other.
 17. The method according to claim 9, wherein each ofthe depositors has assigned thereto a main deposition direction whichextends inclined by not more than 30 degrees relative to a plane formedby the carrier.
 18. A device for producing a cylindrical body, saiddevice comprising a deposition assembly having a plurality of seriallydisposed depositors which are connected to medium supply lines supplyinga starting substance, and which is movable over a closed path ofmovement including at least one path of deposition extending along acarrier which is supported to be rotatable about a longitudinal axisthereof, wherein the path of movement comprises a first loop causing aright-hand twisting of the medium supply lines, and a second loopcausing a left-hand twisting of the medium supply lines.
 19. The deviceaccording to claim 18, wherein neighboring depositors of the depositionassembly are maintained at a predetermined distance in a range of 5 cmto 50 cm from one another, and the deposition assembly and the path ofmovement have lengths related to one another such that during travelthrough the deposition path a first depositor of the deposition assemblyfollows a last depositor at a distance within the range of thepredetermined distance.
 20. The device according to claim 18, whereinthe first loop is traveled through in a predetermined direction ofrotation, and the second loop in an opposite direction of rotation. 21.The device according to claim 20, wherein the first loop and the secondloop have a joint path of deposition.
 22. The device according to claim20, wherein the loops have a crossing point in common and each has atleast one path of deposition.
 23. The device according to claim 18,wherein the first loop and the second loop have equal lengths.
 24. Thedevice according to claim 18 wherein the path of movement comprises aclosed single loop which is traveled through by the burner assembly atleast once as the first loop and at least once as the second loop in thesame direction of rotation, and further having a structure displacingthe medium supply lines or a medium collection line branching into themedium supply lines in such a manner that the medium supply lines or themedium collection line extend to the deposition burners during amovement sequence, alternatingly arriving from one side of the closedsingle loop and from the opposite side of the single loop.
 25. Thedevice according to claim 24, wherein the medium supply lines or themedium collection line can be displaced through the path of movement.26. The device according to claim 24, wherein the medium supply lines(9) are bundled into a medium collection line (33) which branches at abranch point (37) into the medium supply lines (9) connected to thedepositors (4).
 27. The device according to claim 24, wherein thedepositors of the deposition assembly are distributed throughout thesingle loop.
 28. The device according to claim 18, wherein at least onefurther carrier rotating about a respective longitudinal axis thereof isprovided along the path of movement, and that the path of movementcomprises, extending along each further carrier, a respective depositionpath.
 29. The device according to claim 28, wherein the longitudinalaxes of the carriers extend in parallel with one another.
 30. The deviceaccording to claim 29, wherein a distance of the longitudinal axes ofthe carriers opposite to one another along the path of movement can beadjusted.
 31. The device according to claim 18, wherein stationaryadditional heaters are provided in areas adjacent ends of thecylindrical body.
 32. The device according to claim 18, wherein each ofthe depositors has a central axis and that each of the depositors isrotatably supported about the central axis in a mount connected to thepath of movement.